1. Technical Field
The invention relates to the field of gamma-ray detectors, and more particularly to detectors based on Compton scattering.
2. Background Art
There are presently two main design formats for gamma-ray imaging detectors or telescopes: coded aperture mask or Compton scattering configurations.
Coded aperture detectors, such as that taught in U.S. Pat. No. 5,036,546 to Gottesman, et al., have been used to image gamma-ray sources, but do not perform well above 0.3 MeV of energy due to the radiation punching through the aperture either by having no interaction or Compton scattering within the aperture and then depositing the remainder of its energy at the detector plane, thus making the aperture “optically thin” or transparent thereby destroying the system's energy resolution and contrast. This degrades and eventually destroys the image, but the image degradation can be mitigated by adding thickness to the aperture, which additional thickness in turn carries a severe weight penalty and also distorts the image.
Another known approach is to make the coded aperture out of solid state, active detector material, such as from germanium (HPGe) or cadmium-zinc-telluride (CdZnTe) or scintillator such as sodium iodide (NaI) or cesium iodide (CsI), and use the signal that is generated whenever a gamma-ray interacts in the aperture as a veto pulse, essentially instructing the signal processing electronics to ignore the event. However, this results in a significant loss of detection efficiency.
Therefore, coded apertures are rarely used to image gamma-rays above 0.3 MeV when Compton scattering becomes significant.
The second major gamma-ray telescope design comprises Compton scattering telescopes, which utilize the Compton scattering effect that happens when a photon interacts with an electron. The energies of the outgoing photon and electron, along with the angle at which the scattered photon leaves the point of interaction, allow determination of the energy and direction of the original photon or gamma-ray to within a circular cone.
A Compton scattering telescope consists of two detector planes, each level consisting of gamma-ray detecting material such as scintillator (i.e. NaI or CsI), or a solid state detector (i.e. HPGe or CZT). Information from the detectors at both planes is used to determine the interaction points in the two planes and the energy deposited in the detectors at both.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.